Method op making multi-break fabric



United States atent s claims. (Cl. 21a- 74) The present invention is adivision of application Serial No. 129,081, filed August 3, 1961, andrelates to a system of fibers having 'controlled strength and stretchcharacteristics. More specifically the present invention provides anarrangement of fibers such as glass fibers which are disposed in apredetermined pattern so as to constitute a mat or fabric having apredictable stretch and strength characteristic in all or inpredetermined directlons.

It is well known tha-t many fibers, both organic and inorganic havecharacteristics which make such bers desirable for incorporation asreinforcement in impregnated or laminated materials. Metal bers, -forexample, have high strength but low elasticity characteristics. Thepresent invention provides a fabric and method of forming an elasticmaterial using nonelastic reinforcement. While glass 'fibers are used inthe specific example lgiven herein it will be recognized that otherfibers possess similar characteristics and could be used in like manner.

Glass fibers have many desirable characteristics for certain purposes.They possess good electrical insulating properties, 'high strength toweight ratio, `high thermal resistivity and are 'resistant to oils,acids and corrosive atmospheres. Glass fibers do not, however, possessany appreciable elasticity and hence, fabric woven from such fibers willnot st-rentch in order to conform to shapes having, for example, doublecu-rvatures. This characteristic presents a problem when fabrics aremade up of woven glass fiber impregnated wit-h rubber or any othermaterial. Such Ifabrics, if not biased, are unusually st-rong andpossess good electrical insulating characteristics but do not conform toshapes hav-ing ourvat'ures requiring stretchability.

It is also desirable to provide a material in the form of a mat orfabric providing a multi-break material which will give or Abreakcertain fibers on initial tension and will maintain its continuitythrough the medium of a second set of fibers until a predeterminedpercent of elongation fis reached whereupon a third set of fibers isrelied .upon for strength and continuity. In this manner material may befabrica-ted having predictable stretch characteristics in which aninitial .impact will cause the material to give by breaking a certainset of fibers but in which the impact will be contained by a highstrength, controlled elasticity final set of fibers. Additional sets offibers may be provided if desired.

Materials have been designed :heretofore utilizing woven glass fiberimpregnated with rubber or other suitable compound. In order to givesuch materials some degree of stretchability the glass liber fab-ric isinserted on the bias. This type of material has a degree of flexibilitybut the fabric usually must be spliced along its length because of thebias fabric, also the width of the fabric decreases appreciably when thematerial is elongated.

According to the .present invention there is provided a mat or fabriccomprising a first system of glass fiber yarns which are larranged in acurved pattern with a second system of warp yarns knitted to retain the:glass fiber yarns in -their predetermined pattern within the mat orfab-ric. The third warp yarn system may be of a different materialcontaining less geometric extensibility and different strengthcharacteristics than the fibers used in the first system. The elongationof the fabric can be controlled d-uring impregnation or coating and whenthe material must be stretched to conform to a desired shape certain ofthe warp yarns will break to permit the material to assume the desiredconfiguration. The ultimate strength of the material is not adverselyaffected by this breaking of certain warp yarns since the glass fibersforming lthe first system and constituting the principal strength of thereinforcement are still present in continuous form. Purthermore, thewarp yarns, while broken and not continuo-us over great lengths of thefabric, are present and do add to the overall strength of a coated orimpregnated material. Thus, the present invention provides a meanswhereby the desirable characteristics of `glass fibers may beincorporated Iin a material having the additional desirablecharacteristic of stretchability at the desired time.

The present invention finds application as a laminating media where itis desirable that the fabric give slightly under an initial impact butthat the ultimate strength of the material be high to preventpenetration by the impacting object. The formability of the inventionlends itself to products having double curvatures.

An object of the present invention is to provide a fabric or mat havingmultiple lbreak characteristics.

Another object of the present invention is to provide a fabric or mathaving a plurality of systems of fibers including glass fibers, thevarious systems of fibers having varying strength and elasticcharacteristics so that one set of fibers yields under a predeterminedtension without adversely affecting the ultimate strength of thematerial.

Still another object -of the present invention is -to provide aninsulating material having a plurality of systems of fibers impregnatedor coated therein, including glass fibers, the material beingstretchable by virtue of breaking one or more sets of fibers, the glassfibers forming the ultimate strength of the reinforcement remaining incontinuous form.

Other objects and many of the attendant advantages of the presentinvention will become more fully apparent upon consideration of thefollowing detailed specification in connection with the accompanyingdrawings wherein:

FIG. l is a plan view of One embodiment of a fabric according to thepresent invention and,

FIG. 2 is a knitting diagram of the fabric shown in FIG. l.

The present invention comprises a plurality of individual systems offibers which are arranged in a predetermined pattern so as to constitutea mat of set pattern and having controlled strength and elongationcharacteristics.

A fabric according to one embodiment of the invention, is shown inFIG. 1. It can be seen that this fabric is `composed of warp yarns 1 and2 which form a support for the sinusoidally curved yarns 3.

The particular fabric shown is made on a warp knitting machine and theknitting diagram for this particular fabric is shown in FIG. 2. It canbe seen that the yarn 1 is knitted, being wrapped around the needlesalternately in opposite directions. The yarn 2 is passed on either side`of the needle in each course. T he yarn 3 is laid in the warp yarns andis shifted laterally in each course in alternate directions so as tohave a sinusoidal form as shown. In the particular example disclosed theyarn 1 is 40 denier polyester, the yarn 3 is 150/ 2/ 2 glass fiber andthe yarn 2 is 900/1/2 glass fiber. The fabric disclosed in FIG. 1 may beimpregnated with a material such as a silicone rubber when used as atape. Since the fibers are of a controlled thickness and the pattern offibers is generally uniform throughout the length of the fabric, thetape will be of uniform thickness throughout. When such a material iswrapped .around an irregularly shaped object, the yarn 2 willinitiallybreak for the reason that, in the particular fabric disclosed, thesefibers are glass and in this design have a straighter configurationwhereas the fibers 1 are of polyester and pos- 1`sess greaterelasticity. Thus, the yarns 2 comprise a i first system of fibers whichbreak to give the reinforced i material a degree of elasticity. Ifgreater extensibility is i required than is derived from a breaking ofthe yarns l 2, the yarns 1 of polyester may also break and thereinforced tape may 'be stretched until the fibers 3 are i extendingsubstantially longitudinally of the tape. strength characteristics ofthe impregnated material are i not adversely laffected by lthe breakingof the warp yarns since these yarns are still in the tape and theultimate j strength of the tape is based on the presence of the glass lfibers 3.

The

It should be recognized that the specific pattern ,of the fabric may bevaried to suit varying operational requireis only necessary that theseyarns be supported by the knitted warp yarns and be disposed in apattern to give the resulting fabric the desired ultimate strength andextensibility characteristics.

It will be noted that none of the yarns in this disclosed embodimentextend across the entire width of the material. This prevents wickingoccurring across the width of lany fabric so constructed and where slitor coated it does not destroy the integrity of the material.

It is also possible to -construct a fabric in accordance with thepresent invention wherein the yarns used to retain the ultimate strengthfibers in place during manufacture of the impregnated material may besubsequently removed from the material. That is to say, the yarns 1 and2 which retain the yarns 3 in a predetermined pattern may be made of amaterial which by subsequent chemical treatment will be dissolved sothat the fabricated material will contain only the yarns 3. It is alsowithin the realm of the present invention to thermally fuse the warpyarn after the material is impregnated so as to provide a materialhaving substantial elasticity Iand possessing the strengthcharacteristics of tape reinforced with glass fibers.

It is also possible according to the present invention to break theyarns 2 by passing the impregnated tape between a pair of differentialrollers, the second pair being driven at a greater speed than the firstpair so -that the tape is tensioned therebetween. This controlledtension will bre-ak the yarns 2 and give the tape the desired degree ofelasticity.

It can be seen that the present invention provides a fabric in thenature of a matwherein the strength and elongation chara-cteristics arecontrolled and readily predictable. According to this general embodimentone or more systems of warp yarns are used to retain one or moresinusoidally or otherwise disposed systems of glass fibers in place andthese retaining systems break under` tension, thereby providing thematerial `with a certain elasticity and the ability to conform to shapesrequiring stretch in more than one direction. The remaining unbrokenyarns provide the ultimate strength of the material and these yarns aremaintained in continuous form` up to the ultimate strength points of thematerial.

Obviously many modifications and variations of the present invention arepossible in light of -the above teachings. What is claimed as new anddesired to be secured by Letters Patent is:

We claim:

1. The method of forming a stretchable tape comprising the steps offorming a fabric having glass fibers forming a first system of yarnsextending in a sinuous curved pattern warpwise of the fabric, a secondsystem of glass fiber yarns extending warpwise'and a third system ofyarns` knitted to retain said first and second system of yarns toproduce a nonstretchable fabric, impregnatingl fiber yarns extending in`a generally zig-zag pattern in the fabric, said glass fiber yarnsproviding a non-elastic fiber reinforcement, the fabric being formedwith a second system of knitted fibers, impregnating the fabric with anelastic material, disrupting the second system of knitted fibers,permitting the first system of glass fiber yarns and elastic impregnantto elongate with the glass fiber yarns extending in a substantiallystraight line.

3. The method according to claim 2, `wherein the disrupting step isachieved thermally.

References Cited by the Examiner UNITED STATES PATENTS 3,127,306 3/1964Turton et al. 66-202 X MERVIN STEIN, Primary Examiner.

DONALD W. PARKER, Examiner.

L. K. RIMRODT, Assistant Examiner.

2. THE METHOD OF FORMING A STRETCHABLE TAPE HAVING GLASS FIBER YARNSTHEREIN AS REINFORCEMENT COMPRISING THE STEPS OF FORMING A FABRIC HAVINGA FIRST SYSTEM OF GLASS FIBER YARNS EXTENDING IN A GENERALLY ZIG-ZAGPATTERN IN THE FABRIC, SAID GLASS FIBER YARNS PROVIDING A NON-ELASTICFIBER REINFORCEMENT, THE FABRIC BEING FORMED WITH A SECOND SYSTEM OFKNITTED FIBERS, IMPREGNATING THE FABRIC WITH AN ELAS-